Water purification and filtration systems often include ultrafiltration membranes that, over time, accumulate colloidal and suspended particles, which leads to membrane fouling. Many water filtration systems have a backwash cycle to backwash the upstream side of the filtration membrane to remove any of the accumulated reject materials from the feed water to reduce fouling. However, many existing systems use an alternative flush liquid or feed water for backwashing purposes, rather than the already filtered water, in order to reduce premature fouling. Further, many existing systems also use a tank or accumulator to store the ultra-filtered water until needed at the point of use. Over time, bacteria can be produced in the tank, resulting in unsafe drinking water being provided to the user if there is no post-filter provided to clean water being directed out of the tank. Also, most water filtration systems with a backwash cycle require the use of power because of their dependency on either electronically controlled valves, or pressurized gas for backwashing, which makes ultrapure drinking water difficult to acquire in areas with unreliable power systems or with no power at all.
Not only do existing filtration systems require electricity or an additional power source to operate during the backwash cycles, but power is also required during other operational cycles, such as a service cycle and a tank fill cycle, which results in additional operational costs. Also, many purification and filtration systems require multiple accumulator tanks. Typically, one accumulator tank is used to provide water for a backwash cycle, and another tank is used to provide purified water to the point of use, thus adding additional manufacturing costs to the overall system. Additionally, many systems, such as reverse osmosis systems, generate a significant amount of waste water which is inefficient and costly, especially for point of use and residential purification and filtration systems. Lastly, conventional purification and filtration systems typically remove viruses and bacteria from the service water prior to being stored in the system's tank. Thus, there is a higher potential for the service water to be unsafe for drinking due to bacteria that may have been produced in the tank.
One known system discloses an automatic flushing and cleaning system for membrane separation machines such as reverse osmosis machines having plural modules or membranes. Cleaning may be by way of reducing the pressure to allow the membrane to relax, by the injection of air or inert gas to provide turbulence, and/or by injection of flushing liquid which may include chemical cleaning additives. Pumps, automatic valving, and pressure controls are provided, along with a complete time operated electrical sequencing system whereby desired purging, flushing and cleaning cycles are automatically undertaken at periodic intervals or in response to one or more preferred conditions.
Another system provides a membrane filtration system for the separation of solute, colloidal particles, and suspended matter from solutions. The membrane filtration system includes an operation mode and a backwashing mode. A process pump provides suction or negative pressure to the process side of a separation module allowing filtrate to flow from the system tank to the membrane during the backwashing mode, while keeping the filtrate stream separate from the process stream, thereby requiring the user of electrical power to operate the backwash mode.
Similarly, a membrane filtration system uses pump speed controllers to control flow rate and pressure during both a filtration cycle and a backwash cycle. The pump speed controllers operate by changing the frequency of AC current delivered to the pump motors, which changes the flow rate by changing the speed of the pump motor. While pressure and flow pulses are provided throughout the filtration and backwash cycles to dislodge foulants from the membrane, the filtration system requires the use of electrical power. Additionally, the filtration system requires two storage tanks, namely, one for backwash fluid and another for permeate water.
Another system provides a filter backflushing system including an accumulator containing a pressurized bladder which propels a supply of backwash fluid contained within the accumulator in a reverse direction through a filter element to remove clogging contaminants from the filter element. The system only includes a single filter element for the permeate water to flow through prior to storage in the accumulator tank. No other filters are used to clean the permeate water that flows from the accumulator tank to the point of use.
Therefore, it would be desirable to provide a system and method that addresses one or more of the needs described above. More particularly, it would be desirable to provide a system that uses a single accumulator tank capable of simultaneously providing backwash fluid for a first filtration membrane, such as an ultrafiltration membrane, and ultrapure water to a point of use. It would also be desirable to provide a filtration system that mechanically (i.e., requires no power) provides backwash that is a higher transmembrane pressure then the filtering transmembrane pressure, which is caused by opening a faucet which creates a large pressure drop. A system that provides biologically safe drinking water by removing viruses before the water enters the accumulator tank and removing bacteria after the water leaves the accumulator tank is also desirable. Also, providing an ultrafiltration membrane as a prefilter to a microfiltration membrane to protect the microfiltration membrane from fouling is also desirable, as well as a system that uses less waste water than RO systems on the point of use level.